<!DOCTYPE HTML>
<html>

<head>
  <script type="text/javascript">
    function getnum() {
      var mynode = document.getElementsByName(myt);
      alert(mynode.length);
    }
  </script>
</head>

<body>
  <input name="myt" type="text" value="1">
  <input name="myt" type="text" value="2">
  <input name="myt" type="text" value="3">
  <input name="myt" type="text" value="4">
  <input name="myt" type="text" value="5">
  <input name="myt" type="text" value="6">

  <br />
  <input type="button" onclick="getnum()" value="看看有几项？" onclick="getnum()" />
</body>

</html>